teraflops

teraflops - a terraform ops tool which is sure to be a flop

teraflops aims to provide an integrated experience for deployment workflows which involve both terraform and NixOS - similar to that of NixOps. teraflops uses the excellent colmena deployment tool to do most of the heavy lifting, so the following example should look somewhat familiar if you have ever used colmena.

{
  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
    teraflops.url = "github:aanderse/teraflops";
  };

  outputs = { nixpkgs, teraflops, ... }: {
    teraflops = {
      imports = [ teraflops.modules.hcloud ];

      meta = {
        nixpkgs = import nixpkgs {
          system = "x86_64-linux";
        };
      };

      machine = { pkgs, ... }: {
        deployment.targetEnv = "hcloud";
        deployment.hcloud = {
          server_type = "cx11";
          location = "nbg1";
        };

        environment.systemPackages = [ pkgs.htop ];
      };

      # if desired you can write terraform code directly inside your teraflops modules
      terraform = {
        backend.s3 = {
          bucket = "mybucket";
          key = "path/to/my/key";
          region = "us-east-1";
        };
      };
    };
  }
}

Usage

The teraflops tool has a number of high level commands that often resemble the NixOps CLI.

# prepare your terraform state in the current working directory
teraflops init

# applies all terraform state and deploys your NixOS configuration
teraflops deploy --reboot --confirm

# perform some operational commands
teraflops ssh-for-each -- df -h
teraflops scp machine:/root/.ssh/id_ed25519.pub .

# NixOS introspection
teraflops repl
teraflops eval '{ nodes, ... }: builtins.attrNames nodes'

Additionally there are two low level subcommands which get out of your way and let you use the tools you're used to: terraform and colmena.

# 'teraflops tf' is a direct passthrough to terraform
teraflops tf init
teraflops tf apply

# 'teraflops nix' is a direct passthrough to colmena
teraflops nix repl
teraflops nix apply --reboot

Deployment arguments

terapflops implements the set-args command from NixOps. Referencing the example from NixOps:

{
  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
    teraflops.url = "github:aanderse/teraflops";
  };

  outputs = { nixpkgs, teraflops, ... }: {
    teraflops =
      { maintenance ? false }:
      {
        machine =
          { config, pkgs, ... }:
          { services.httpd.enable = maintenance;
            ...
          };
      };
  };
}

You can pass deployment arguments using the set-args command. For example, if we want to set the maintenance argument to true in the previous example, you can run:

teraflops set-args --arg maintenance true

Special arguments

In addition to the regular nix module inputs and those defined by calls to the set-args command the following arguments are available to teraflops modules:

outputs: The fully evaluated terraform output values. Generally these aren't as useful in teraflops as they are in terraform because the teraflops eval command has full access to a resources argument which accounts for most use cases in terraform.
resources: The fully evaluated terraform resource set, which includes resource, data, module, etc... objects representing the full state of your deployment.
tf: A minor helper which is most useful for the tf.ref function it contains which is used to create terraform references, just like in terranix.

NOTE: Both outputs and resources will be null when a teraflops module is evaluated for the purpose of generating terraform code in order to avoid recursion.

Comparison

colmena

colmena is entirely stateless
teraflops can make full use of terraform state

terranix

terranix builds a high level nix api on top of terraform which includes full build time validation
teraflops exposes terraform directly to you through nix, sacraficing build time validation in favor of run time validation in order to make the development of various teraflops backends (like digitalocean, hetznercloud, linode, lxd, etc...) extremely quick and easy in the spirit of RFC42
terranix focuses on terraform code generation and leaves NixOS integration to the user
teraflops provides full and direct integration with NixOS

NixOps

NixOps builds a high level nix api on top of various cloud providers which includes full build time validation, though requires extensive python development for every backend desired, many of which do not yet exist
teraflops leverags terraform for all of this work so as long as a terraform backend exists it is near trivial to create a teraflops module for it
NixOps development is has lagged for a number of years, though apparently there are plans to bring it back!
teraflops is a young project and relies on established software like colmena, terraform, and nixos-infect to provide all major functionality making teraflops already quite a capable tool

Implementation

A very quick python script I hacked together which isn't great. Don't look at the code yet... really 😅

bbigras / teraflops